Conventional portable printers use a roll of wound media, such as paper or label stock, which is loaded into the printer such that the media from the roll will properly feed and align with a thermal print head for printing. These rolls have tubular cores and portable printers typically have a pair of holder members each with an extending cylindrical shaped surface for engaging into a roll core, thereby limiting mounting of such rolls with cores of a inner diameter which can frictionally engage the outer diameter of the cylindrical shaped surface. Often such holder members are part of a roll positioning mechanism with respect to printing elements of the printer. One example of such a portable printer is shown in U.S. Pat. No. 6,609,844, which has a rack and pinion gear centering mechanism having two rotational spindle members for mounting a roll.
Often rolls are crushed during transportation or storage and will lack a circular cross-sectional shape for proper rotational mounting when loaded in the portable printer, resulting in misaligned rolls which can negatively effects printer performance. This is due to such crushed rolls having a non-circular (oval or eye shape) cross-sectional shaped core, rather than the needed circular cross-sectional shape for mounting on holders or spindle members. Although a user can attempt to recrush the roll in another dimension to re-circularize the roll, the roll is prone to damage and may still not properly rotationally mount in the printer. Thus, holders or spindle members for mounting rolls are desirable which can be used for different diameter rolls and can automatically reshape (or re-circularize) the ends of core crushed rolls.
Different mechanisms have been developed for supporting a roll of media between two members via insertion into the ends of a roll's tubular core. U.S. Pat. No. 5,813,343 describes a roll mounting mechanism with two holders each having a cylindrical head with axially spaced concentric steps to accommodate the inner diameters of different dimension tubular cores, such holders are spring urged towards each other. The front of each concentric step extends to a truncated conical form. U.S. Pat. No. 6,536,696 describes a point of sale printer having pair of spherical bearing members each extending into the ends of a central core of a roll. U.S. Pat. No. 4,821,974 describes a large document printer having two spindles shafts each with a conical surface and a hub assembly having compression springs for urging the each shaft's conical surface into the ends of a media roll core. None of these patents provide spindle members for rotationally mounting a roll which are reversibly mountable in the printer to accommodate different diameter core rolls and have surfaces capable of automatically re-circularizing the ends of a crushed roll core when such holder or spindle members are urged together into the roll core.